Known in the art is a use of sulfur hexafluoride (SF.sub.6) as a refrigerant (U.S. Pat. No. 1,778,033). The advantages of said refrigerant are a sufficiently high refrigeration efficiency and environmental safety.
However, sulfur hexafluoride has a substantially high factor of vapor pressure within the range of industrial refrigeration at temperature from -20 to 35.degree. C. This hinders utilization of said refrigerant in a medium-temperature refrigeration equipment.
To the prior art is know a number of working sulfur hexafluoride (SF.sub.6) based mixtures for refrigeration equipment, having a lower vapor pressure at appropriate conditions, than sulfur hexafluoride.
Simultaneously, presence of sulfur hexafluoride in conventional refrigeration equipment ensures a reduction of energy consumption of apparatuses and technological processes owing to the abnormally low specific heat ratio of sulfur hexafluoride SF.sub.6 (1.02-1.04).
For comparison, the same ratio for octafluoropropane (C.sub.3 F.sub.8) is 1.13, while for octafluorocyclobutane it is 1.07.
Known in the art is, for example, a working mixture for refrigeration equipment; comprising sulfur hexafluoride (SF.sub.6) and difluorochloromethane (CHC1F.sub.2) (U.S. Pat. No. 3,642,639).
The aforementioned working mixture for refrigeration equipment has an essentially higher refrigeration capacity than each component thereof, taken separately. Said working mixture can be most efficiently utilized in low-temperature refrigeration equipment within the boiling point range from -25 to 40.degree. C.
At the same time, the conventional working mixture comprises a fluorine-containing component giving the mixture ozone depleting properties.
As is known, under international agreements on the Earth's ozone layer protection, refrigerants of such type should be completely taken out of utilization by the year 2020.
There exists several approaches to develop ozone-friendly refrigerants. Particularly, known is an ozone-friendly working mixture for refrigeration equipment, consisting of two fluorocarbons, namely, of octafluoropropane (C.sub.3 F.sub.8) and octacyclobutane (C.sub.4 F.sub.8), molecules of which do not comprise chlorine atoms (U.S. Pat. No. 1,781,279).
The aforementioned working mixture meets modern requirements of ozone safety.
However, the component concentration range, most efficient from the point of reducing energy consumption, provides a high boiling point or a working mixture, which hampers the mixture utilization in household and industrial low- and medium-temperature refrigeration equipment. At the most efficient relationship of octafluoropropane and octafluorocyclobutane of 40:60, respectively, the boiling point is -19.degree. C., while at the relationship of 36:85, it is -22.degree. C.
Also known in the art is an ozone-friendly working mixture for refrigeration equipment, comprising sulfur hexafluoride (SF.sub.6) and fluorocarbon, such as trifluoromethane (CHF.sub.3) (U.S. Pat. No. 3,719,603, 1973).
In contrast to the previously mentioned working mixture, said mixture can be most efficiently utilized only in a special-purpose refrigeration equipment operating at a temperature lower than -70.degree. C. As is known, the range of temperatures at which household refrigeration equipment and air conditioners operate most efficiently, is several tens of degrees higher.
Furthermore, a molecule of trifluoromethane (CHF.sub.3) posseses a relatively low dissociation energy, lower than 370 kilojoule/mole, which makes said component of the mixture insufficiently stable with respect to destruction under a long maintenance of the refrigeration equipment. Due to destruction of trifluoromethane and appearance of nonrecombining decomposition products as a result of chemical reactions, conditions of normal maintenance of refrigeration equipment are violated, which can cause a failure thereof.